An e-mail reply to Mike, G3XDV concerning my settings of the Spectrogram software would involve a lot of settings data. I have decided to publish this information via my homepage. First of all I would like to compliment the author of the software for the fine job and for his service to Radio Amateurs by adapting his software for our needs. This freeware software will run on Windows95 and 98 platforms only. For more information please contact the author:

An other reason for publishing the following data is the fact that it is not possible to change Digital signal processing settings during an input scan. I hope this information will help other Radio Amateurs finding their favourite settings. The new feature to set the spectrum colours is helpful. I have found out that a sharp break in the colour spectrum is most helpful when the noise level is just above the colour change level. This gives an optical representation of the sound levels divided into two groups, below and above noise. The red level has also the most vivid contrast to the light blue in the colour spectrum. Strong signals will appear as yellow horizontal stripes. The 136.7 kHz spectrum without HAM-activity looks like this:

The vertical lines are static (QRN) caused by thunderstorms the horizontal lines are spurious signals emitted by LF radio location systems.

HOW CAN YOU MAKE A SPECTROGRAM?

To get started connect a receiver and tune to the desired frequency. For Slow CW minimal requirements are modes CW (morse code telegraphy signals on/off keying mode A1A) or BFO or Single Side Band USB/LSB/ISB. The audio output of an unmodulated radio signal (carrier) on the desired frequency is set to 800Hz if possible. Connect the line input from your SoundBlaster compatible audio card to the line output of the receiver. Please check audio power levels to prevent damage to your equipement. If the power level is carefully adjusted the headphone output of the receiver may be used. Start the Spectrogram software and start "F3-scan input" on the main file menu. For a start you can use the settings listed below and you can experiment with other settings to find optimal results for your needs. During reception you can adjust the colour intensity via the main file menu option "Color palette" and "F4-scroll display". Signal range is set lower for viewing signals with more or less the same strength. For more dynamic signals choose a bigger signal range. The gain sets the relation between colours and signal strength. If the screen is black or blue increase the gain and if the screen is to yellow or red you may decrease the gain. Again experimenting is the best way to find the optimal settings four your own spectrograms. For more information please read the help-information available via the help menu in the software.

The spectrograms on this page have been made with the following settings:

Morse-code can be red fairly easy when analysing Slow-CW radio signals. You can see an example of a radio transmission by the Amateur station G3XDV on 137.7 kHz, received 09:00 UTC on July 11th 1999. The second audiogram is a transmission by the Amateur station DJ5BV on 137.7 kHz, received 20:30utc on July 16th 1999.

The following spectrograms have been recorded on july 17th 1999 with low 137kHz. band noise conditions. Image number 4) shows dk8kw ending his transmission and g3xdv answering while dj3bv gives CQ a few Herz above this QSO and all signals are clearly visible. The relative signal strength is dj3bv a-32dB; dk8kw at -37dB and g3xdv at -42db. The Loran-C signals are horizontal light blue signals at -50dB. There are also natural radio signals visible with the same relative strength as the Loran-C signals but they appear as curved light blue lines running diagonaly donwards.

Image number 5 shows the sferics conditon over Europe (lightning strikes) on july 17th. Only the south of France and the Baltic had thunderstorms and most of the activity was in the afternoon. The weak radio signals from Amateur radio transmissions in the 136kHz LF band can be completely inaudible because of the static noise caused by lightning.

On july 18th 1999 the spectrogram image 6) was recorded. Local noise shows light blue on the left side of the diagram. Fortunatly the equipment causing the interference (our television set) was turned off and Loran-C lines are visible again. Static noise increased later this day as you can see on the diagram number 7).

A sound file can be down loaded from my site for those who would like to experiment with their own settings and compare with the G3XDV spectrogram above. Please note that the WAV file is really large and it might take a lot of time before you get it over to your computer. The total recorded time is approx. 5 minutes and 52.5 seconds

Disclaimer: Information on this page may be used only at the sole responsibiltiy and at own risk and free will of the user of the information. By using any information on this page you will automatically and totaly agree with this statement.